The use of
Rapid Syphilis Tests
Special Programme for Research & Training in Tropical Diseases (TDR) sponsored by
The use of
Rapid Syphilis Tests
The Sexually Transmitted Diseases Diagnostics Initiative (SDI)
Special Programme for Research & Training in Tropical Diseases (TDR) sponsored by
TDR/SDI/06.1
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Contents
I. What is syphilis and why is it important? . . . .8
II. How is syphilis diagnosed? . . . . 9
III. What is a rapid syphilis test? . . . .1 0 IV. How is a rapid syphilis test performed? . . . . 11
V. How effective is a rapid test in detecting syphilis? . . . .12
VI. When is a rapid syphilis test useful? . . . . 13
VII. How to decide if you need rapid testing for syphilis? . . . .14
VIII. What do rapid test results mean and when do you treat? . . . . 16
IX. What should you consider in purchasing rapid syphilis tests? . . . . 18
X. How do you transport and store rapid syphilis tests? . . . . 20
XI. How do you ensure the quality of your syphilis testing programme? . . . . 22
Appendix 1.Non-treponemal and Treponemal Tests for Syphilis . . . . 24
Appendix 2.Test sensitivity and specificity, and the importance of prevalence in the estimation of predictive values of diagnostic tests . . . . 25
Text Box 1.Global burden of syphilis . . . . 8
Text Box 2.Serological testing for syphilis . . . . 9
Text Box 3.Comparison of non-treponemal vs rapid treponemal tests . . . . 10
Text Box 4.Mean distance to the nearest health facililty . . . .14
Figure 1.Estimated incidence of syphilis: global distribution . . . . 7
Figure 2.How rapid syphilis tests are read . . . . 11
Figure 3.Facility-based approach to assess need for rapid syphilis tests . . . .13
Figure 4.Rapid testing algorithms and treatment of sero-reactive cases . . . .17
C
V
Acknowledgements:
We would like to acknowledge the valuable contribution of many colleagues towards the development of this guide, in particular, Drs Gloria Aguilar, Renette Anselme, Robin Bailey, Ron Ballard, Stuart Berman, John Changalucha, Xiang-sheng Chen, David L. Cox, da Cruz, Marius Domeika, John Douglas, Odalys García, Felizbela Gaspar, Felícia Guzmán, King Holmes, Edward Hook III, Peter Hughes, Jean Joly, Robert Johnson, Mary Kamb, David A. Lewis, Catherine Lindsey, David Mabey, Laurie Markowitz, C. Mpambo, Olive Mtema, Peter Mwaba, Sandy Nérette Fontain, Valdir Pinto, Adele Schwartz Benzaken, Freddy Tinajeros, David Tress, Johannes Van Dam, Suzanne Westman, Yueping Yin, and our WHO colleagues: Drs Bilali Camara, Karoline Fonck, Francis Ndowa, Guy-Michel Gershy-Damet, Dionne Patz, N. Benoit Soro.
The STD Diagnostics Initiative (SDI) received funding from The Bill & Melinda Gates Foundation for this work.
For copies and queries, please contact:
Dr Rosanna Peeling, WHO/TDR E-mail: peelingr@who.int
4 million sub-saharan Africa
4 million South & Southeast Asia
10 000 Australia & New Zealand 140 000
Western Europe
240 000 East Asia & Pacific 370 000
North Africa &
the Middle East 100 000
North America
100 000 Eastern Europe &
Central Asia
3 million Latin America &
the Caribbean
Figure 1
WHO estimates of number of new cases of Syphilis per year
Access to syphilis diagnostics is limited
in regions of high disease burden
Syphilis is a curable infection caused by a bacterium called Treponema pallidum. This infection is sexually transmitted, and can also be passed on from a mother to her fetus during pregnancy. As a cause of genital ulcer disease, syphilis has been associated with an increased risk of HIV transmission and acquisition.
Most persons with syphilis tend to be unaware of their infection and they can transmit the infection to their sexual contacts or, in the case of a pregnant woman, to her unborn child. If left untreated, syphilis can cause serious consequences such as stillbirth, prematurity and neonatal deaths. Adverse outcomes of pregnancy are preventable if the infection is detected and treated before mid-second trimester.
Early detection and treatment is also critical in preventing severe long term complications in the patient and onward transmission to sexual partners. Congenital syphilis kills more than one million babies a year worldwide but is preventable if infected mothers are identified and treated appropriately as early as possible. The World Development Report cites antenatal screening and treatment for syphilis as one of the most cost-effective health interventions available:
Health Cost per DALY*
Interventions saved (US$)
Expansion of Childhood Immunizations US$ 2-20
Oral rehydration therapy US$ 7-28
Antenatal syphilis screening (8% prevalence) US$ 4-18 Prevention of mother to child transmission
of HIV (15% prevalence) US$ 50-200
* DALY = Disability Adjusted Life Years
I. What is syphilis and why is it important?
Text box 1
Burden of syphilis and its impact in pegnancy
The World Health Organization estimates that 12 million new cases of syphilis occur every year (see Figure 1 for distribution of disease burden)
In developing countries, 3-15% of women of child-bearing age have syphilis. About 30% of pregnant women with syphilis will give birth to a dead baby (stillbirth), and another 30% to a live baby with congeni- tal syphilis, a condition with a mortality of up to 50%.
Patients with symptoms and signs suggestive of syphilis (e.g. genital ulcer, skin rash) may be treated presumptively, unless appropriate investigations can be performed.
However, since most patients with syphilis have no symptoms or signs, diagnosis relies on a blood test for the detection of antibodies (see text box 2).
Until recently, serological testing for syphilis has been performed in a lab- oratory with:
1. Trained personnel;
2. Refrigeration for storage of reagents;
3. Electricity to run equipment: refrigerator, centrifuge and shaker Since such facilities are generally not available in remote areas, blood or serum samples have to be transported to regional or central facilities for testing. Results are therefore often available only days or weeks after test- ing. If those who are tested do not return for their results, they are not treated, resulting in a waste of resources, adverse clinical outcomes and continued transmission of infection.
A recent study in Tanzania showed that syphilis was responsible for 50%
of stillbirths, yet only 30% of pregnent women are screened for syphilis in sub-Saharan Africa.
Rapid tests for syphilis are now commercially available. These are simple point of care tests and can be performed outside a laboratory setting with minimal training and no equipment using a small amount of whole blood collected by a finger prick. Hence they can address the problems associated with lack of access to a laboratory and the low patient return rates.
II. How is syphilis diagnosed?
Text box 2
Serological tests for syphilis
•
A non-specific (non-treponemal) test, such as the Rapid Plasma Reagin (RPR) test or Venereal Disease Reference Laboratory (VDRL) test.•
A specific (treponemal) test, such as the Treponema pallidum Hemagglutination Assay (TPHA) or Treponema pallidum Particle Agglutination Assay (TPPA) or FTA-ABSMost rapid syphilis tests currently avail- able are treponemal tests but combination non-treponemal/treponemal tests are under development.
For the purposes of this document, a rapid test is a simple point-of-care test that can be used in all health care settings to allow immediate treat- ment. It is easy to perform and does not require special storage or trans- port conditions. The result should be easy to interpret and ideally, avail- able in 30 minutes. Most rapid syphilis tests are made in a dipstick or cassette format.
Non-treponemal tests such as the RPR can be considered rapid tests as they can provide a result in less than 10 minutes.
However there are important distinctions between currently available non-treponemal test and the rapid treponemal tests as shown in text box 3.
III. What is a rapid syphilis test?
Text box 3
Comparison of non-treponemal vs rapid treponemal tests
Non-treponemal tests:
RPR or VDRL
Advantages - simple to perform - can distinguish between active and past treated infection (anti- bodies wane after effec- tive treatment except for a small number of sero- fast individuals)
Disadvantages - require electricity for refrigerator to store reagent, and for a rotator and centrifuge - cannot be used with whole blood - false negative results can occur with excess antibody (prozone effect) Rapid treponemal tests - simple to perform
-can be used with whole blood, serum or plasma - can be transported and stored at temperatures below 30oC
- no prozone effect
- cannot distinguish between active and past treated infection (antibodies to trepone- mal antigens are retained for years)
More than 20 rapid syphilis tests are commercially available. Although the specific instructions for processing differ, most tests are performed with only 3-4 steps. Figure 2 illustrates the simplicity of these tests:
1. Remove the test from the wrapper and place on a flat surface;
2. Add a specified amount of patient sample (whole blood, plasma or serum) to the sample well S;
3. Add a specified amount of diluent buffer to sample well S;
4. Read the results after a specified time (usually 15-20 mins) as shown in Figure 2: (C=control line; T=test line).
IV. How is a rapid syphilis test performed?
Figure 2
How rapid syphilis test are read?
•
Negative:only 1 line below C
•
Positive:lines below C & T
•
Indeterminate:no lines below C or T
C T
S
C T
S
C T
S
When used according to the manufacturers’ directions, most rapid syphilis tests are effective at detecting syphilis. The Sexually Transmitted Diseases Diagnostics Initiative (SDI), based in the Special Programme for Research and Training in Tropical Diseases (TDR), has evaluated a number of these tests and found them to be appropriate for use in various settings.
The sensitivity of these tests, which is the proportion of people with syphilis that have a positive test result and is hence a measure of the ability of a test to detect infection, ranges from 85-98% compared to a laboratory-based reference standard test such as the TPHA or TPPA.
The specificity of these tests, which is the proportion of people without syphilis that have a negative test result and hence a measure of the ability of a test to exclude infection, range from 93-98% (see Appendix 2 for more details on these issues and the predictive value of these tests).
More information is available at the SDI website:
www.who.int/std_diagnostics
Results of the rapid tests are reproducible only if the tests are stored and performed according to manufacturer’s instructions, including
special attention to expiry dates.
Visit the SDI website:
www.who.int/std_diagnostics
V. How effective is a rapid test in detecting syphilis?
Targeted screening of syphilis for at risk individuals is cost-effective.
Given the potentially serious sequelae of syphilis and increased risk of HIV transmission, the following groups should be targeted for screening:
•
Pregnant women ( to prevent congenital syphilis)•
Individuals with or at risk of STIs•
Sex workers•
Clients of sex workers•
Men who have sex with men•
Injection drug usersALMOST EVERY COUNTRY HAS A POLICY FOR ANTENATAL SCREENING BUT ACCESS TO TESTING IN MOST AFFECTED COUNTRIES range between 30-38% (Gloyd et al 2001)
Once it has been decided that the introduction of rapid tests would be useful in a country or a specific area, it has to be decided to whom this test should be offered and under what circumstances.
VI. When is a rapid syphilis test useful?
Text box 4
Mean distance to the nearest health facility for the poorest fifth of the population
(source: World Development Report 2004)
Country distance in km
Benin 7.5
Bolivia 11.8
Chad 22.9
Haiti 8.0
Madagascar 15.5
Niger 26.9
Tanzania 4.7
Uganda 4.7
Zimbabwe 8.6
Countries that have already established effective syphilis control pro- grammes, including screening for antenatal and high risk populations, may prefer to maintain their program rather than introduce rapid tests.
This decision should be based on a careful assessment of the quality, coverage and efficacy of the current programme.
Points to consider in such an assessment, including the decision to introduce rapid testing for syphilis, are:
•
Access: what is the proportion of persons at risk and pregnant women that have access to syphilis testing? Rapid point of care tests enable countries to increase access to antenatal screening.•
Quality of testing: what is the quality of the testing? Is there an on-going quality control program to monitor and to ensure accurate results?•
Treatment of sero-reactive case: what proportion of persons tested receive their test results and have access to treatment in a time- ly manner (ideally during the same visit)?•
Rapid tests: will introducing rapid testing help improve coverage/access and programme efficacy?VII. How to decide if you need rapid testing for syphilis?
Consider the following steps for a facility-based approach to introduction of rapid tests for syphilis screening (see Figure 3 on the next page):
1. Decide which population groups are to be targeted for screening 2. Decide which facilities are to be
involved to cover the population groups to be tested.
3. Assess the current capacity to conduct syphilis testing.
4. Decisions regarding rapid test introduction will depend on type of facility, capability, and case load.
5. Introduction of rapid tests includes procurement, logistics, training, and quality assurance.
Figure 3
Sample flow chart for this decision making process
Is testing currently available at this facility?
Yes No
Maintain current System (and improve
as necessary)
Introduce Rapid Syphilis Tests Poor
No
Yes Good
Can current System be fixed?
Evaluate quality of testing and
coverage
Since rapid treponemal tests cannot be used to distinguish between active and past treated infection, treatment of all rapid test positive individuals will result in over-treatment. However, given the serious consequences of missed treatment, the benefits of treatment far out- weigh the harm of over-treatment.
Suggested testing algorithms and treatment decisions are shown in Figure 4 (see page 17).
If RPR is not available, test with a rapid test and treat all patients with a positive result.
Where RPR is available and performed well, rapid tests may also have a role:
•
Treatment can be provided on the basis of a positive RPR result alone•
Rapid treponemal tests can be used to confirm a positive RPR result, and treatment would only be given to patients with a confirmed positive result•
Rapid tests can also be used for screening; for patients with a positive rapid test result, RPR can be used to confirm active infection.In patients with discrepant non-treponemal and rapid test result, if confirmation with a reference standard test is not an option or re-test in 6 weeks, treatment should be given.
Special considerations
Pregnant women:
In pregnancy, all patients with a positive test should be treated, regard- less of treatment history in a previous pregnancy. This is important because of the possibility of a new infection since the last pregnancy, and of the very severe consequences of untreated infec- tion in this group.
High risk/vulnerable populations:
In high risk populations, all patients with a positive rapid treponemal test should be treated. The most important and unresolved issue in this group is the frequency of testing and treatment in patients that already have had a positive test. Further studies are needed in this area.
Rapid point-of-care tests are currently under development that would be better indicators of active infection and should help resolve this issue with regard to treatment decisions.
VIII. What do rapid test results mean and when do you treat?
Figure 4
Suggested testing algorithms and treatment decision points
positive negative Blood
Rapid test
treat
treat treat
positive
positive
positive RPR
retest in 6 weeks negative
negative Blood
Rapid test
No RPR testing available When RPR testing is available
The performance and reproducibility of some commercially available rapid treponemal tests have been evaluated by the WHO. Details and results of the evaluation can be found at the SDI website:
www.who.int/std_diagnostics
•
Test Performance: given the serious consequences of a missed diagnosis, and rarity of adverse side effects of over-treatment, test sensitivity is more important than specificity for screening. If the rapid tests are to be used as confirmatory tests, then high specificity is important.•
Ease of use: the number of processing steps, whether it can use whole blood, and need for accurate timing will influence extent of training and supervision required.•
Conditions of use: in humid conditions, the selection of rapid tests individually packaged in moisture-proof pouches is strongly recom- mended.•
Conditions of storage: most rapid syphilis specify storage temperatures between 4-30ºC. If the clinic temperature is above 30ºC, periodic quality control checks to ensure the ongoing validity of the tests are important.•
Shelf life: longer shelf life reduces the pressure on the supply chain and the probability of wastage of expired tests; a minimum of 18 months is recommended in remote, poorly resourced areas.•
Price:rapid tests can be purchased through the WHO Bulk Procurement Scheme at between US$ 0.19 to US$1.0.Choosing an appropriate rapid syphilis tests
Major considerations in test selection include:
•
test performance•
ease of use, including format of the test (e.g. cassette, dipstick, card)•
shelf-life and temperature stability in intended conditions of storage and use•
requirement for additional supplies such as pipettes•
cost (including transport, training)Rapid test products and manufacturers
WHO does not certify or recommend any specific product, but makes data on the performance and utility of rapid tests available to all UN member states and on its website.
IX. What should you consider in purchasing rapid syphilis tests?
Tendering and the availability of product information Together with considerations of the sensitivity and cost of a product, it is useful to know the quality of manufacturing processes, the long- term viability of a company, and the consistency of production.
This will influence the ability of a company to replace a product should the received lot fail the quality control process, and will ensure long-term supply of a product to minimize the need for re-training.
Purchasers should request the following information from manufacturers during the tendering process:
1. Real-time temperature stability data on the product, and accelerated data on the purchased lot;
2. Evidence of successful operational use, or good quality field data on the product;
3. Long-term viability of manufacturer (to ensure continuity of supply);
4. Availability of product support;
5. Provision of sample products for assessment and testing for ease of use;
6. Agreement for replacement of products which fail agreed quality control procedures;
7. Box sizes appropriate to the rate of use of tests in the intended area, to minimize storage time in poor conditions and limit the need to split boxes.
Point 3 implies that the place of manufacture of rapid tests should be disclosed to the purchaser if rapid tests are re-labeled.
Purchasers should also consider evidence of good manufacturing prac- tice (e.g. GMP or ISO certification; ISO13485:2003 is a standard specific for medical devices).
Clarity of packaging of the end product is essential to allow identifica-
Exposure to high temperatures is probably a major contributor to poor performance, particularly during transport and storage. Transfer from the manufacturer, and road transport within a country, are particularly vulnerable times. High humidity can rapidly degrade rapid tests, includ- ing prolonged exposure to humidity after removal from the envelope or if the envelope is damaged.
Most manufacturers recommend rapid tests storage between 4ºC and 30ºC. Expiry dates are generally set according to these conditions.
If kits are stored at temperatures exceeding the recommended limits, it is likely that the shelf life of the rapid tests will be reduced and sensitivity lost prior to the expiry date. The maintenance of temperatures between 4ºC to 30ºC for shipment of rapid tests is essential. Transport of rapid tests from manufacturers and within countries should be monitored as follows:
Shipping from manufacturers
1. Before shipping, the manufacturer contacts consignees with details of air waybill numbers, airline carrier, flight number, numbers of con- tainers, and expected arrival time. These details should be sent by e-mail and followed up by facsimile.
2. The shipper (air carrier) is notified of temperature storage require- ments by the manufacturer in writing and by clear markings on cartons and related documents. (Stowage of the shipment close to the skin of some aircraft may result in freezing.)
3. The manufacturer initiates shipment only when the consignee con- firms the shipping notification is received.
4. Consignees then arrange to have customs agents or other personnel on site to receive materials – shipments are moved immediately to moderate temperature storage (less than 30º C if possible). Avoid
X. How do you transport and store rapid tests?
Ground transportation
5. Ground transportation during any stage of delivery is carried out with- out delay and with attention to ambient temperature while the vehi- cle is moving and if parked. Avoid leaving rapid tests in vehicles parked in the sun.
Storage
6. Storage at central and final field facilities should be within the manu- facturer’s specifications.
7. Maximize the time rapid tests are stored in centralized, controlled conditions; minimize uncontrolled storage in remote areas. Smaller box sizes may help achieve this.
8. Select a cool peripheral storage location; thatch roofing may be cool- er than iron, maximize shade, consider evaporative cooling cabinets.
Transport and storage at temperatures above 30ºC is sometimes
unavoidable, as in many remote locations where rapid tests are intended for use. Monitoring of sensitivity of rapid tests at appropriate intervals is therefore essential. WHO is developing recommendations for quality assurance to address these issues.
The quality of the testing programme depends on the quality of the test kits and the proficiency of the end-users at performing the tests.
A number of steps should be considered in the evaluation of the test- ing programme:
Quality Control on validity of test kits
Since temperatures that the test kits are subject to during transport may affect the sensitivity of the tests, the sensitivity of rapid tests should be checked at a central laboratory with a well-characterized quality control panel on receipt from the manufacturer, and periodical- ly throughout the recommended shelf life. Users of test kits sent to peripheral health centres should be alerted of any depreciation of test quality during that time.
Proficiency of users
Adequate training and supervision of end-users of rapid tests should be integrated as far as possible into existing health worker training and quality assurance schemes.
Concise clear Standard Operating Procedures (SOPs) should be pre- pared in local languages for the health workers trained to perform the test. Instructions for processing and interpretation should be clear, including biosafety issues associated with finger pricking procedures.
Health workers using the tests should be trained and assessed, and systematically monitored on test processing and interpretation.
XI. How do you evaluate the quality of your testing programme?
Appendixes
Since it is not possible to culture Treponema pal- lidum on artificial media, the detection of serum anti- bodies is often used as surrogate markers of T. pal- lidum infection. As mentioned previously, these tests fall into 2 categories:
Non-treponemal tests
Non-treponemal tests such as the VDRL (Venereal Disease Research Laboratory) or the RPR (Rapid Plasma Reagin) detect antibodies to a lipoidal anti- gen, resulting from the interaction of the host with T. pallidum or from T. pallidum itself. These tests are widely used because of their low-cost and are rela- tively easy to perform. However, non-treponemal tests may give false positive results. Hence positive treponemal test results may need to be confirmed using treponemal tests. Some common conditions associated with false-positive test results are listed below:
Potential causes of cross-reactivity Infectious causes
•
Malaria•
Tuberculosis•
Viral fevers•
Trypanosomiasis•
Leprosy•
Other treponemes Non-infectious causes•
Drug addiction•
Connective tissue disease•
Pregnancy•
Advanced age Treponemal TestsThe most frequently used tests are the TPHA (T. pallidum hemagglutination), the TPPA or the FTA-ABS. When positive, these tests are considered evidence of a previous or current infection with T. pallidum. These are laboratory-based tests that require equipment and trained staff to perform.
They will remain positive for life in a person that previously had syphilis. A new generation of these tests in an ELISA format is now commercially avail- able. These tests can be batched for high throughput testing.
Appendix 1. Non-treponemal and treponemal tests for syphilis
Sensitivity and specificity of a test are not the only parameters of importance in evaluating its appropri- ateness in a given population. The prevalence of the disease is important in assessing its positive and neg- ative predictive value. The predictive value of the same test can differ between countries and between different populations in the same country as showed in the following table.
Given a population of 10,000 with the prevalence of syphilis estimated at 1, 5, 10, and 15% and at a test sensitivity of 85, 90 and 95% and specificity of 95%, the positive predictive value (PPV) and negative predictive value (NPV) and the number of false negative and false positive tests are as follows:
Appendix 2. Test sensitivity and specificity and the importance
of prevalence in the estimation of predictive value of diagnostic tests.
Prevalence Sensitivity Specificity PPV* NPV* #False #False
negatives positives
1% 85% 95% 15 100 15 495
1% 90% 95% 15 100 10 495
1% 95% 95% 16 100 5 495
5% 85% 95% 47 99 75 475
5% 90% 95% 49 99 50 475
5% 95% 95% 50 100 25 475
10% 85% 95% 65 98 150 450
10% 90% 95% 67 99 100 450
10% 95% 95% 68 99 50 450
15% 85% 95% 75 98 225 425
15% 90% 95% 76 98 150 425
15% 95% 95% 77 99 75 425
The results presented in the presented in the preceding table are not specific to rapid tests but can be applied to all diagnostic tests.
* PPV = positive predictive value
* NPV = negative predictive value
os:WHO/TDR/Andy Craggs-Rosanna Peeling • Design and Layout:Lisa Schwarb TDR/World Health Organization
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